Reliability design method and Limit state design methodfor Maritime structures● Organization

ECOH CORPORATION● Department

Design Department● Presenter

Noriyoshi UEHARA● TEL/FAX/ e-mailTEL +81-3-5828-2186 / FAX +81-3-5828-2176 / e-mail uehara@ecoh.co.jp

INTRODUCTION
The software for maritime structure design consists of the reliability design method for theoverall design and the limit state design method for the detailed design. The former
employs probabilistic approaches. The latter calculates the three levels of design waves forthe ultimate, serviceability, and fatigue limit states, and examines the safety of designed
structures against these waves.
With this software, the stability and safety of the rational design of maritime structures
can be achieved.
DEVELOPMENT PROCESS
Traditional design of maritime structures ( e.g. breakwater ) has been made deterministically with the concept of safety factors. The reliability design method is based on the theoryof probability and maintains the probability of failure below a certain allowable value. Thismethods enables engineers to design maritime structures economically with sufficientmargin of safety.
The limit state design method uses the three levels of design stresses under the ultimate
limit state, the serviceability limit state and the fatigue limit state, which require detailed
stress analysis for the safety of structures.
The software of this design method has been developed to respond to several project
requests.
KEY POINTSKey points of design methods for maritime structures.
●Reliability design method
This method takes account of the uncertainties of actions on and resistances of thestructure and evaluates the deformation and/or damage quantitatively.
*Expected sliding distance of caisson type breakwaters*Relative damage of concrete armor units●The limit state design method
Determination of three levels of design waves for three limit state conditions and the safetyanalysis of structures.
*Use of the limit states (the ultimate, serviceability, and fatigue limit states)*Estimate the design waves *3-D stress analysis●Drawing the standard cross section
The standard cross sections of structures are drawn with CAD software.
APPROVAL/CREDITABILITY
ECOH CORPORATION is continuing to promote the quality of software based on theexperience and achievements of design projects for maritime structures.

0.8

1.4

Case1(SF=1.0）
Case2(SF=1.2)
Case3(SF=1.27)
Case4(SF=1.25)

0.6
0.4

Allowable
許容滑動量0.3m
sliding distance

0.2
020

40

Tetrapod 32t
テトラポット32t型
Tetrapod
40t 40t型〃
Tetrapod
50t 50t型〃〃
Tetrapod
60t 64t型

1.2

6080

Expectedrelative damage
期待被災度
N

Expectedsliding distance
期待滑動量（m） (ｍ)Graphical Outputs with Design software

100

1.0
0.8
0.6 Design

relative

0.4 設計被災度N
damage0=0.3
0.20（年）
Design 耐用年数
working life(year)

Fig. 1 Expected sliding distance of caisson
breakwater designed with several levelsof safety factor against design working life
(Example of reliability design method)

Fig. 3Standard cross section of
curved slit caisson breakwater

10203040

Design 耐用年数（年）
working life(year)
Fig. 2

Expected relative damage of Tetrapodsof different sizes against designworking life
(Example of reliability design method)

Fig4

Bending moment of structuralelements of caisson( with 3D stress analysis )50